Hydraulic lash adjusters are well known devices for use in valve trains for maintaining near zero valve clearance in an internal combustion engine. The hydraulic lash adjusters are typically situated between the camshaft and each of the engine's gas exchange valves. The lash adjuster comprises a hollow steel cylinder that encases an internal piston. The piston is biased toward its outer limit to lengthen the hydraulic lash adjuster with a spring. Together, the cylinder and the piston define a fluid chamber filled with oil. When the gas exchange valve is closed, the fluid chamber is free to refill with oil. As the camshaft lobe enters the lift phase of its travel, the hydraulic lash adjuster is compressed and an oil inlet valve is closed. Because oil is nearly incompressible, the compression renders the lash adjuster effectively solid during the lift phase. However, because some clearance must be maintained between the piston and the cylinder of the hydraulic lash adjuster, some oil will leak along this annular clearance during each cycle. As the camshaft lobe travels through its peak, the load is reduced on the lifter piston, and the internal spring returns the piston to its neutral state so that the fluid chamber can refill with oil.
U.S. Pat. No. 4,184,464 shows a hydraulic lash adjuster that shows a capture groove defined in the outer surface of the piston so that leaked hydraulic fluid during the compression phase can be captured and recirculated within the hydraulic lash adjuster. Hydraulic lash adjusters that predated the '464 patent typically included no recapture or recirculation groove so that all of the leaked oil would spill from the hydraulic lash adjuster and be returned to sump. In some newer applications, neither full recirculation nor zero recirculation hydraulic lash adjusters addressed new potential problems in these engines.
The present disclosure is directed toward one or more of the problems set forth above.